The remarkable human facility with social cognition depends on a foundational ability to reason about other people based on an understanding of their minds. The specific aims of the work proposed here are to i) test whether we have special ("domain specific") cognitive and neural mechanisms for detecting and reasoning about other minds, ii) discover the functional organization of this system (i.e., what are its main components?), and iii) characterize the processes that go on, and the representations that are extracted, in each of these components. Our experiments will use fMRI to identify regions in human temporal and frontal cortex that are involved in understanding other minds. The purpose of this work is not simply to discover the anatomical locus of these regions, but to use fMRI to identify and characterize the functional components of the system. In particular, in Part I the Domain Specificity Hypothesis will be tested, by asking whether any brain regions are more active in conditions that involve detecting or reasoning about other minds than in control conditions that do not involve other minds but that are matched for complexity, difficulty, and logical structure. We will also test whether any candidate cortical regions implicated in detecting other minds are engaged whenever the relevant stimulus information is present, independent of the task the subject is asked to carry out (the Automaticity Hypothesis). Parts II and III describe experiments investigating the functional architecture of the system identified in Part I, by testing whether this system consists of a single mechanism that is involved in all aspects of perceiving and reasoning about other minds (the Single Component Hypothesis), or whether it consists of several functionally dissociable components, each instantiated in a different cortical region (the Multiple Components Hypothesis). These experiments will also test specific hypotheses concerning the function of each component. The experiments proposed here constitute the first broad- based effort to use neuroimaging to characterize the functional architecture of one of the core components of human cognition: detecting and reasoning about other minds. Progress on the experiments outlined here will provide a solid foundation for future research exploring the recruitment of these core systems in everyday social behavior, the development of these systems in childhood, and the disruption of this system in neurological patients, autism, and psychopathology.